Device for supplying lighting panels



July 15, 1958 G. DIEMER 2,843,804

DEVICE FOR SUPPLYING LIGHTING PANELS Filed Jan. 29, 1954 9 Power Suppgy United States Patent 2,843,804 DEVICE FOR SUPPLYENG LIGHTING PANELS Gesinus Dienier, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application January 29, W54, Serial No. 407,079 Claims priority, application Netherlands February 3, 1953 7 Claims. (Cl. 315-178) The present invention relates to an electro-luminescent lighting panel device.

It is known that a few substances, more particularly specially treated luminescent substances, such as, for example, Zinc sulphide, cadmium sulphide, and mixed crystals thereof, emit visible rays under the action of a variable electric field. On this phenomenon are based the so-called lighting panels which consist of two plane electrodes made of electrically conductive material and having a thin layer of such an electroluminescent substance interposed between them as dielectric. At least one of the electrodes is transparent. On the side of this electrode the panel emits light, if an alternating voltage of sufficient intensity, for example, of some hundreds of volts, is set up between the electrodes.

An electro-luminescence which is useful in practice is generally produced only if the frequency is comparatively high, for example, of the order of some thousands of cycles per second. Consequently, direct connection to the electric power supply is usually not possible, so that a device is included which raises the power supply frequency. This may be a frequency multiplier or oscillator comprising one or more amplifier tubes which are supplied with rectified supply voltage, if the power supply is an A. C. supplyv p Such devices are complicated and have a low efficiency. The present invention provides a device for supplying a lighting panel which with high efficiency transforms the power supply voltage into alternating voltage at optimum frequency and voltage. It can be used not only with an alternating voltage supply, but also with a direct voltage supply.

In accordance with the present invention, an oscillator is provided with feedback and its frequency is substantially determined by a capacity and a resistance. Thus, an alternating voltage having steeply rising wave edges is produced which is very advantageous for supplying the lighting panel. It is possible for the oscillator to be supplied from the alternating voltage power supply directly, that is without interposition of a rectifier. It has been found that the fact that in this event the oscillations are interrupted periodically raises no difficulty in providing a device which is advantageous in practice.

Preferably inductive feedback is used, an inductance being connected in three-point connection to the anode, the control-grid and the cathode of a controlled discharge tube. The control-grid of the tube is connected through a capacity to one end of the inductance and through a resistance to the cathode. The dimensions of the different elements are such that the frequency set up is substantially determined by the said capacity and resistance. In this event, the lighting panel may be connected in parallel with the inductance or a part thereof as a capacity. In order to adapt different lighting panels to the device in optimum manner it is desirable for the inductance to be provided with a number of tapping points, in which case the cathode of the tube may be connected at will to one of said tapping points by means of a switching member. If the lighting panel has a large surface area, it may be advantageous to divide it in a number of sections which are connected in series. Moreover, in this event it is often easier to obtain a good adaptation for the high frequencies. The cathode may be directly heated in that it is also connected directly to the alternating current power supply in series with a capacitor of suitable capacity.

In order that the invention may be readily carried into effect, it will now be explained with reference to the accompanying drawing, in which:

Fig. l is a schematic diagram of an embodiment of the device of the present invention;

Fig. 2 is a graphical illustration aiding in the explanation of the operation of the device of the present inventlon;

Fig. 3 is a schematic diagram of another embodiment of the device of the present invention; and

Fig. 4 is a schematic diagram of still another embodiment of the device of the present invention.

In Fig. 1, reference numeral 1 designates a lighting panel, which may be looked upon as a capacitor. It is connected in parallel with an inductance 3 which is connected in three-point connection to an anode, a controlgrid and a cathode of a triode 2 which acts as an oscillator. The inductance 3 may consist of a coil comprising a core made of substantially ncn-conductive magnetic material. The inductance 3 has a tapping point 4 connected to one of the power supply terminals 8 and also through a capacitor 6 to one end of the cathode, which is also the filament, of the triode. The inductance 3 may have one or more additional tapping points; for example, a tapping point 4, with which a switch arm 10 may cooperate in order to adapt different lighting panels to the device in optimum manner. The other end of the cathode is connected to the other one of the power supply terminals 8. The power supply is supposed to be an alternating voltage supply. One end of the coil 3 is connected directly to. the anode, the other end being connected through a capacitor 5 to the control-grid of the triode.

The control grid and the left hand end of the cathodehave a resistor '7 interposed between them. The cathode of the tube 2 may be indirectly heated.

The dimensions of the different elements a'resuch that the frequency set up is not determined by the parallel combination of the inductance and the capacity of the lighting panel, but by the capacity of the capacitor 5 and the resistor 7. For this purpose the capacitor 5 should be smaller than in the usual threepoint connection. The elements are advantageouslydimensioned as follows:

If the capacity of the. capacitor mined by the inductance 3 and the capacity 1.

If the device is supplied with alternating voltage, interruptions of the oscillations determined by the resistor and the capacity will occur during the half period in which the potential across the anode is negative. Upon a proper choice of the parts these oscillations are produced for substantially the whole time during which the anode is positive. For some time after the cessation of these oscillations, however, oscillations will be produced in the circuit 1, 3 the frequency of which is determined by the inductance and the capacity of the lighting panel 1.

capacity of the 5 is made suificiently; large, a frequencyis set up which is substantially deter- In Fig. 2, the line a represents the shape of the curve of the produced supply voltage in the case of the anode being at a sufficiently high positive potential. Towards the end of the positive half-period it changes into the curve [2 which represents a damped oscillation the frequency of which is determined by the inductance and the capacity of the panel. This remains active during a short period of time subsequent to the passage through zero. The curve c is the envelope which is substantially sinusoidal.

It has been found that the peak-shaped voltage :1 having steep edges is advantageous for the electroluminescence. The effective value of the voltage produced may be 200 volts in the case of a supply of 220 volts, 50 cycles per second.

Fig. 3 shows an arrangement in which the lighting panel 1 is connected between the anode of the tube and the cathode supply conductor which is directly connected to the power supply. In this case, the voltage at oscillator frequency which is active across the lighting panel is somewhat lower than in the arrangement of Fig. 1. On the other hand, the supply voltage at 50 cycles per second is invariably set up across the panel 1. Thus, there is less flicker and also, when the triode becomes blocked, the panel continues to luminesce, although with lower intensity.

If, in addition, a switch 9 is included in the filament lead, the triode can be put out of circuit while the power supply voltage continues to be active across the panel with the result that this continues to luminesce with decreased intensity.

Fig. 4 shows a symmetrical arrangement comprisng two oscillator tubes 11 and 12 which are active alter-' nately. The filaments are supplied with alternating current through two identical capacitors 15 and 16 connected in series. The panel 1 is connected between the anodes. The coils 13 and 14 may be wound on a common core. In this arrangement flicker can be substantially avoided.

In addition, the devices described have the advantage that they consist of standardized parts and occupy very little space.

While the invention has been described by means of specific examples and in specific embodiments, I do not Wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. An electro-luminescent lighting panel device comprising a lighting panel comprising an electro-luminescent material and means for energizing said luminescent material, said means comprising an oscillatory circuit for producing an oscillatory voltage having steeply rising wave edges and having an electron discharge tube and a feedback circuit connected thereto and including a capacitor and a resistor, said capacitor and said resistor having values at which the frequency of the voltage of said oscillatory circuit is substantially determined by the magnitudes of the resistance of said resistor and the capacitance of said capacitor, means for supplying an operating voltage to said oscillatory circuit, and means for applying said oscilltory voltage from the output of said oscillatory circuit to said lighting panel.

2. A device as set forth in claim 1, wherein said supply means includes an alternating voltage source directly connected to said oscillatory circuit.

3. A device as set forth in claim 1, wherein said feedback circuit is an inductive feedback circuit.

4. A device as set forth in claim 3, wherein said oscillatory circuit includes an inductance connected across said lighting panel, and wherein said electron discharge tube includes an anode, a cathode and a control-grid, said inductance being connected at a first point to said anode, at a second point to said control grid through said capacitor, and at a third point to said cathode, said resistor being connected between said control-grid and said cathode.

5. A device as set forth in claim 4, wherein said inductance includes a plurality of tappings and further including a switch member for selectively connecting one of said plurality of tappings to said cathode.

6. An electro-luminescent lighting panel device comprising a lighting panel comprising an electro-luminescent material and means for energizing said luminescent material, said means comprising an oscillatory circuit for producing an oscillatory voltage having steeply rising wave edges and having an electron discharge tube including a directly heated cathode and a feeback circuit including a capacitor and a resistor, said resistor and capacitor having values at which the frequency of the voltage of said oscillatory circuit is substantially determined by thet magnitudes of the resistance of said resistor and the capacity of said capacitor, a second capacitor, means for applying an alternating voltage to said directly heated cathode through said second capacitor, and means for applying said oscillatory voltage from the output of said oscillatory circuit to said lighting panel.

7. An electro-luminescent lighting panel device comprising a lighting panel comprising an electroluminescent material and means for energizing said luminescent material, said means comprising first and second oscillatory circuits for producing an oscillatory voltage having steeply rising wave edges, each of said circuits having an electron discharge tube and a feedback circuit including a capacitor and a resistor, said capacitor and said resistor having values at which the frequency of the voltge of said oscillatory circuit is substantially determined by the magnitudes of the resistance of said resistor and the capacitance of said capacitor, means for supplying an operating voltage to each of said'oscillatory circuits, and means for applying the oscillatory voltage from the output of each of said oscillatory circuits to said lighting panel.

References Cited in the file of this patent UNITED STATES PATENTS 2,121,829 Seaman et al. June 28, 1938 2,142,633 Dey et al. Jan. 3, 1939 2,291,467 Goldberg July 28, 1942 2,347,715 Spencer May 2, 1944 2,488,169 Browner Nov. 15, 1949 2,566,345 Mager Sept. 4, 1951 2,694,785 Williams Nov. 16, 1954 

